1. Field of the Invention
The present invention relates to capacitors and, more particularly, to a capacitor formed as part of an intermediate substrate.
2. Description of Related Art
Two prior art references of interest include a patent, Japanese Patent Application Laid-Open No. 2003-142624, and a publication entitled “Development of low inductance thin film decoupling capacitor,” Kazuaki Kurihara, Electronics installation technology, Vol. 19 (2003), No. 1, page 50.
In integrated circuit devices such as a CPU and other LSI, which operate at high speeds, power supply lines are allocated to plural circuit blocks within the integrated circuit such that the supply lines branch from a common power supply. When plural devices in the circuit block switch at high speeds at the same time, a large current is immediately induced from the power supply, so that a resultant deflection in the power supply voltage produces noise which propagates to the respective circuit blocks through the power lines. This problem has been addressed by providing each circuit block with a decoupling capacitor to lower the power supply impedance. This approach is effective in suppressing the propagation of noise between circuit blocks due to the aforementioned deflection in the power supply voltage. Further, a bypass capacitor for removing external noise, such as surge noise, in the form of AC filtering is provided in the same connection configuration in some cases.
In case of a large-scale integrated circuit such as a CPU, the number of circuit blocks is large, and the quantities of power terminals and ground terminals have also been increasing, so that the distance (spacing) between the terminals has been correspondingly decreasing. The decoupling capacitor mentioned above must be connected to each power line leading to each circuit block. Because of this, it is difficult to connect each capacitor to an integrated circuit containing a large number of densely packed terminals from the viewpoint of the corresponding installation demands. Further, this approach is contrary to the current trend toward smaller size devices.
With this background, turning to the two references mentioned above, these references disclose a thin film decoupling capacitor in which a ferroelectric thin film and a metallic thin film are layered, and a number of capacitor terminals connected individually to the densely packed terminals on the integrated circuit are created using photolithography technology. In high frequency operation (particularly at frequencies of 100 MHz or more) the above-mentioned problem with respect to noise due to a deflection in the power supply voltage is likely to occur at the time of high speed switching. The reason for this is that the ratio of inductive reactance term of the power supply impedance increases, and decreasing as much as possible the distance between the power terminal connected to the decoupling capacitor and the ground terminal is effective in reducing the power supply impedance. Further, when the inductance at the terminal portion increases, the inductance is coupled with the capacitive component of the decoupling capacitor so as to produce a resonance point. This is a problem because of the decrease in the bandwidth necessary to produce a sufficient reduction in impedance. Thus, this is another problem that needs to be solved. In this regard, manufacturing a thin film capacitor having a small distance between the terminals using photolithography techniques as described above contributes not only to a reduction in size of the device but also to a reduction in the power supply impedance and an increase in bandwidth, which is the original purpose.
However, the abovementioned patent discloses a configuration in which the thin film capacitor is constructed by itself in the form of an intermediate substrate. With this configuration, because the stiffness of the thin film capacitor is not high, when the main substrate to which the capacitor is connected is a substrate comprised mainly of polymer material (such as a motherboard or an organic package substrate) which forms an intermediate substrate of the second stage, when a manufacturing process is used which involves thermal hysteresis, such as soldering reflow, the solder may peel off or the thin film capacitor itself may be damaged due to the insufficient stiffness thereof. In the latter regard, this damage may occur because the capacitor is incapable of absorbing the difference in linear expansion coefficient between the semiconductor device and the main substrate.